from qiskit.quantum_info import Statevector
from math import sqrt
def create_bell_statevector() -> Statevector:
    """ Return a phi+ Bell statevector.
    """
    return (Statevector.from_label("00") + Statevector.from_label("11")) / sqrt(2)

def check(candidate):
    result = candidate()
    solution = (Statevector.from_label("00") + Statevector.from_label("11")) / sqrt(2)
    assert result.equiv(solution)

    print("OK")

if __name__ == '__main__':
    check(create_bell_statevector)